The W-CDMA (Wideband Code Division Multiple Access) based packet communication system needs to allocate radio resources. Thus, the W-CDMA based packet communication system has a plurality of communication states so as to effectively use radio resources in accordance with the amount of communication data or in accordance with the accommodation number (the number of users), the communication states including a Cell-DCH state, a Cell-FACH state, a Cell-PCH state, and a packet idle state.
The Cell-DCH state is a communication state in which a mobile phone terminal can communicate with the network at high speed. In the Cell-DCH state, communication channels are allocated to individual users. Moreover, in the Cell-DCH state, uplink and downlink communication channels are allocated on both the mobile phone terminal side and the network (hereinafter abbreviated as the NW) side. A mobile phone terminal needs to always communicate with the network so as to maintain uplink and downlink communication channels. Thus, the amount of current consumed by the mobile phone terminal in the Cell-DCH state is large compared to that in the other communication states.
In the Cell-FACH state, uplink and downlink communication channels are shared by other mobile phone terminals. The data communication speed in the Cell-FACH state is slow compared to that in the Cell-DCH state. However, the Cell-FACH state does not need to always maintain an uplink communication channel. Instead, in the Cell-FACH state, an uplink communication channel which is referred to as the RACH (Random Access Channel) can be allocated when necessary. Thus, the amount of current that is consumed by the mobile phone terminal in the Cell-FACH state is small compared to that in the Cell-DCH state. However, even in the Cell-FACH state, a downlink communication channel is always maintained (opened).
The Cell-PCH state is a communication state that takes place when there are no communication packet data. The Cell-PCH state is a standby state that is maintained until communication packet data occur. In the Cell-PCH state, a downlink communication channel is intermittently allocated. Thus, the amount of current that is consumed in the Cell-PCH state is very small compared to that in the Cell-FACH state.
In the Cell-PCH state, since a downlink communication channel is intermittently allocated, the Cell-PCH state is very similar to the packet idle state that will be described later. However, in the Cell-PCH state, an RRC connection is set up between the mobile phone terminal side and the NW side. Thus, the mobile phone terminal communicates with a particular base station in a semi-communication state. As a result, the Cell-PCH state has an advantage in which a call connection process is quickly performed when packet communication resumes in response to occurrence of communication packet data, specifically, a communication state transition from the Cell-PCH state to the Cell-DCH state is more quickly performed than that from the packet idle state to the Cell-DCH state.
The packet idle state is a communication state in which the foregoing RRC connection is lost. In the packet idle state, although radio resources between the mobile phone terminal and the NW are released, Packet Data Protocol Context (hereinafter referred to as the PDP Context), which is a packet communication protocol, is maintained. Thus, when the packet communication resumes, the PDP Context does not need to be set up again. Instead, only the RRC connection is performed. Consequently, the process time, which is the period from when the state of communication with network is set to the packet idle state until the packet communication resumes, is slightly short compared to the process time during which the packet communication starts up.
The NW side uses the foregoing individual communication states so as to effectively employ communication resources. Specifically, the NW side has a system that causes each mobile phone terminal to perform a communication state transition to a communication state in which it does not waste a lot of radio resources based on a predetermined parameter. The parameter includes the amount of packet data to be communicated and idle packet communication time.
Normally, when packet communication starts up, the mobile phone terminal performs the packet communication in the Cell-DCH state. Thereafter, as the amount of packet data to be communicated decreases, the NW causes the mobile phone terminal to perform communication state transitions to the Cell-FACH state, the Cell-PCH state, and the packet idle state.
In contrast, if the amount of packet data to be communicated increases, the NW causes the mobile phone terminal to perform a communication state transition to any one of these communication states depending on the amount of packet data to be communicated or the communication time of the packet communication. In this case, generally, the NW causes the mobile phone terminal to perform a communication state transition to the Cell-DCH state.
The data amount or communication time of the packet communication, which is a parameter based on which the NW causes the mobile phone terminal to perform a communication state transition, is a characteristic value of the NW side. However, this parameter may differ area by area.
As described above, generally, the NW controls communication state transitions for the mobile phone terminal. The mobile phone terminal cannot control communication state transitions. Thus, even if the mobile phone terminal is not performing packet communication with the NW, the mobile phone terminal needs to maintain a communication state in which more current is consumed than that in the other communication states. In other words, a problem in which the mobile phone terminal cannot perform communication state transitions to communication states in which its current consumption is low occurs.
Patent Literature 1 describes a communication system that allows a mobile phone terminal to perform communication state transitions to other states. In the communication system described in Patent Literature 1, the mobile phone terminal controls communication state transitions between the Cell-DCH state and the Cell-FACH state based on the communication history.
On the other hand, the Fast Dormancy function that allows a mobile phone terminal to control communication state transitions has been established by the 3rd Generation Partnership Program (hereinafter referred to as the 3GPP).
The Fast Dormancy function is a function that causes a mobile phone terminal to notify the NW of an event of a release of the RRC connection (only the RRC connection is released, but the PDP Context is maintained) if an idle packet communication state continues for a predetermined time.
This function allows a mobile phone terminal to perform communication state transitions from each communication state directly to the packet idle state. Thus, it is expected to accomplish a communication state transition control taking into consideration the reduced amount of current that is consumed by the mobile phone terminal.